Why a building's floors need to be separated to prevent fire travel
NFPA Journal®, January/February 2010
Fire aggressively travels upward. For this reason, the Life Safety Code® is very concerned about protecting openings between floors through which smoke, heat, and flames may travel upward. Vertical openings include all holes in a floor, including pipe, conduit, cable, and duct penetrations; shafts; atria; and similar openings between floors.
Section 8.6, “Vertical Openings,” specifically addresses the protection of vertical openings. Section 8.6.1 requires all floors to be constructed as a smoke barrier. That is, all penetrations must be sealed so that smoke cannot flow between floors. Of course, the floors may also require some fire resistance, depending on the construction requirements found in Section -1.6 of each occupancy chapter and local building code requirements.
Sections 8.6.3 and 8.6.4, which address the construction of a shaft if a hole is cut in the floor, require that the shaft walls have a one-hour fire-resistance rating where the shaft connects three stories or fewer and a two-hour fire-resistance rating where it connects four stories or more. The code requires that all penetrations be sealed to prevent smoke travel between floors or that a shaft be constructed around the holes and that all penetrations of the shaft wall be protected to maintain the wall’s fire-resistance rating.
The Life Safety Code allows only four specific types of floor openings. We will refer to the first, found in Section 8.6.6, as a “mini-opening,” as the code limits it to three stories. Mini-openings are often found in entrance lobbies where the building designer wants to make a grand entrance open to the second or third floor. The code requires that the three floors open to the hole between the floors be protected with automatic sprinklers. All areas not open to the hole between floors must be separated by one-hour fire-resistive construction or equivalent construction. In addition, all occupants must have access to at least one exit to which they do not have to travel through the area open to the hole in the floor. In all, eight protection items must be met for this hole in the floor.
The second floor opening the code permits is an atrium, as noted in Section 8.6.7. An atrium requires complete automatic sprinkler protection, a one-hour or equivalent separation of areas not open to the atrium, and an analysis of the atrium’s need for smoke control. Six specific protection items are listed for atria.
The third code provision to permit a hole in the floor is found in Section 22.214.171.124. Actually, this provision does not allow a hole in the floor, but rather an enclosure at the top or bottom of the hole through the floor. For example, a stairway between two floors that is not an exit may be open to one of the two floors. A full shaft enclosure is not required, as the stair is not an exit and penetrates only one floor.
The fourth provision for a hole between two floors is sometimes referred to as a convenience opening. This opening cannot be used as an exit and cannot be open to a corridor. It might be used as a convenience stair between two floors of a building where those two floors are occupied by the same tenant.
The Life Safety Code requirements for separating floors to prevent fire travel are quite clear. Holes open between floors must meet one of the four provisions noted above. Fire spread between floors is of major concern and the strict provisions in the code for protecting vertical openings reflect that concern.
Chip Carson, P.E., is president of Carson Associates, Inc., a fire engineering and code consultancy. He is a former member of NFPA's Board of Directors.